Impact driven tool with replaceable cutting point

ABSTRACT

The shaft and replaceable cutting point of an impact driven tool utilize half an ellipse as the outline of both the external cross-sectional configuration of the driving end of the shaft and the internal cross-sectional configuration of the recess in the tip. The tip is frictionally retained on the shaft driving end for effecting a driving connection therewith.

United States Patent Swisher [151' 3,655,244 [4 1 Apr. 11, 1972 [541IMPACT DRIVEN TOOL WITH REPLACEABLE CUTTING POINT [72] Inventor:

[73] Assignee: International Tool Sales, Inc., Bridgeport,

Conn.

22 Filed: July 30, 1970 [21] Appl.No.: 59,438

James A. Swisher, Easton, Conn.

[52] U.S. Cl ..299/91, 279/103, 287/126, 299/94 [51] Int. Cl. ..E2lc37/26 [58] Field of Search ..299/91-94; 287/119, 126; 279/102, 103;175/409, 414-419 [56] References Cited UNITED STATES PATENTS 3,336,0818/1967 Ericsson ..299/94 X 2,080,526 5/1937 Bedford ..279/96 UX3,027,953 4/1962 Coski ..175/414 X 2,654,573 10/1953 Annesley ..175/40-9X 1,471,461 10/1923 Harmon ..175/414 X Primary ExaminerErnest R. PurserAttorney-Wooster, Davis and Cifelli [57] ABSTRACT The shaft andreplaceable cutting point of an impact driven tool utilize half anellipse as the outline of both the external cross-sectionalconfiguration of the driving end of the shaft and the internalcross-sectional configuration of the recess in the tip. The tip isfrictionally retained on the shaft driving end for effecting a drivingconnection therewith.

8 Claims, 4 Drawing Figures Patented April 11, 1972 3,655,244

INVENTOR. James /7. SZl/LS/lfi? IMPACT DRIVEN TOOL WITH REPLACEABLECUTTING POINT BACKGROUND OF THE INVENTION The invention relates to animprovement in impact driven tools having a replaceable, frictionallyretained cutting point.

Such a tool is used in combination with a pneumatically powered hammer,drill, or the like, which forcibly drives the tool into reinforcedconcrete, rocks, and other similar hard materials.

Already known in the art are impact tools having replaceable,frictionally retained tool points. In order to attain a suitablereliable friction fit between the tool point and the driving end of thetool shaft, both the exterior of the driving end and the interior of therecess in the tool point are provided either with one set of taperedinterfitting surfaces or two sets of variously tapered interfittingsurfaces. Those which utilize one set of tapered surfaces have thedisadvantage that when too much taper is used, unwanted separation ofthe cutting point results and, on the other hand, when a generallyshallow taper is used, the cutting point is too tightly interfitted withthe driving end of the shaft and can only be forcibly removed from suchend which oftentimes results in breaking of the point or the tool shank.Exact dimensioning of the taper angle of such surfaces is difficult and,in addition, the cutting point of such impact tool, of necessity,requires an overall relatively thick-walled construction to adequatelyabsorb and transmit the percussive forces necessary to drive the tool.Those impact tools which utilize more than one set of tapered surfacesemploy cutting points which include a portion of relatively thin-walledcon-' SUMMARY OF THE INVENTION The object of the invention is toovercome the above disadvantages and to provide an improved percussiontool which provides a positive driving connection between thereplaceable point and the tool shank, which are rupture-free andsecurely connected in operation.

Such percussion tool comprises a shaft with a drive end surface formedby a half ellipse of revolution and a cutting point with a recesssurface formed by a half ellipse of revolution releasably interfittinglyengaging the drive end surface for effecting a driving connectionbetween the shaft and the point formed by continuously curved fullymating surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of apercussion tool according to the invention, illustrating the shaft andreplaceable tip in disassembled condition but axially aligned forassembly;

FIG. 2 is a composite fragmentary view of the tool of FIG. 1, withportions removed to show the respective cross-sectional configurationsof the driving end of the shaft and the recessed ti FIG. 3 is acomposite fragmentary view similar to FIG. 2, showing the tip fullyseated and frictionally retained on the shaft;

FIG. 4 is a composite fragmentary view of a known percussion tool withreplaceable tip.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsin which like reference numerals index like parts and with attentionfirstly directed to FIG. 1, the percussion tool embodying the presentinvention and indicated generally at 10, initially is seen to comprisean elongated shaft section 12 having a conventional hexagonal bitter end14 arranged to be operatively received in the usual tool holding memberof a pneumetically powered jackhammer or the like. A peripheral collar16 bounds the bitter end 14 and is operative to properly lengthwiseposition the tool 10 in the tool holding member of the power hammer.Provided intermediate the driving end 18 of the shaft 12 and the collar16 is a hexagonal extended portion 20 which terminates into a gradualupset 22. The driving end 18 of the shaft has a substantiallysemi-elliptical external cross-sectional configuration, i.e. is formedby a half ellipse of revolution. The shaft is made of a suitably hardmaterial, such as a high speed drill or chisel grade steel.

The cutting point or tip section 24 of the tool 10 is seen to comprise arecess 26 which, as clearly shown in FIGS. 2 and 3, has a substantiallysemi-elliptical internal cross-sectional configuration substantiallycorresponding to that of driving end 18 of the shaft. The upper annularwall section 28 of the tip is relatively thin while its lower contiguouswall secton 30 is relatively thicker and of greater area. The tip 24 isinitially loosely placed onto the driving end 18 (FIG. 2) with the mainaxes of the two sections axially aligned along the line A-A, FIG. 1. Thethin-walled area 28 of the tip is designed such that when initiallyassembled it has an inner upper diameter 32 which is somewhat smallerthan the external diameter of upper portion 33 of the driving end 18.During operation of the tool 10, and due to the axial percussive forcesexerted on the tool 10, the driving end 18 penetrates deeper into thecavity of the tip until percent bearing i.e. full continuously curvedmating between the'respective surfaces of the tip and driving end isachieved (FIG. 3), in which condition the apex 34 of the shankabuttingly engages the extreme innermost end 36 of the recess 26.

During such penetration of the driving end 18 into the tip 24, the upperthin-walled portion 28 of the tip is impactively slightly stretched bydriving end portion 33 and, upon fully seating of the driving end in thetip, wall portion 28 permits a friction or tension retaining action onthis end by exerting radial compressive forces thereon that grippinglyhold the shaft and the tip together, even under the most adverseconditions, including heavy pneumatic hammer driving vibration.

The dimension of the inner diameter 32 of thin-walled portion 28 isfurther advantageous in that it substantially reduces the possibility ofa stress raiser forming in adjacent shank portion 33 when the shaft endis fully seated in the tip.

During operation of the tool, and as a result of the maximum matingsurfaces of the tip and driving end, the axial percussive forces exertedon the tip by the shaft have maximum transmission area between therespective surfaces in the region of thick-walled area 30 of the tip andbetween the apex 34 of the shaft and the innermost end 36 of the tip.Such maximum transmission of the tool driving forces is indicated by thearrows in the tip in FIG. 3.

This maximum surface mating between the tip and shaft end furtherprovides maximum transfer areas for and even dissipation of shocks andfrictional heat generated during operation of the tool.

The surfaces of the driving end 18 and recess 26 are dimensioned such asto enable easy initial installation of the tip on the shaft and also itslater removal therefrom. Such surfaces are mathematically generated byintersecting a cone with a plane which forms a half ellipse or parabolawhich is the locus of the points in this particular embodiment. It isself-evident that in addition to such particular half ellipse orparabola other sections may be generated by utilizing differentparabolas, ellipses and hyperbolas, each of which could be used, i.e.revolved to achieve surfaces that lie within the framework of theinvention:

The tip 24 terminates into an apex 38 which constitutes a blade-shapedcutting edge and is configurated such that during operation of the toolthe axial percussive forces are advantageously distributed over anddissipated from the entire width of the cutting edge to preventpremature material failure of the tip.

For practical purposes and by way of example, the tip of the inventioncan be manufactured from AISl No. S1, a Tungstentype shock resistantsteel. With proper heat-treating, the point area of the tip can behardened to a Rockwell hardness of 56-62 Rc-Scale which has been foundextremely favorable for improving the durability of the tip. The shankarea of the tip preferably is of a lesser Rockwell hardness, for example-25 C-Scale, which permits a predetermined interference fit between themating surfaces of the tip and the shaft to be realized without the riskof possible breakage of the tip resulting from an excessive hardness ofthe shank portion of the tip.

The gradual upset 22 of shaft 12 serves to ease the abrupt transitionbetween the larger core diameter of extended hexagonal portion 20 of theshaft and the smaller diameter of upper portion 33 of driving end 18.

By utilizing the semi-elliptical outline for both the externalcross-sectional configuration of the shaft driving end and the internalcross-sectional configuration of the tip recess, considerable advantagesare obtained in addition to those already hereinbefore described. Forexample, as the tip wears and the material properties deteriorate due toshock, frictional heat, abrasion, and the like, the shank moves deeperinto the cavity which enlarges the mating area between the respectivesurfaces and thereby reduces the unit stress. The possibility of stressraiser forming is furthermore greatly reduced as a result of the absenceof abrupt changes in the diameters of the mating surfaces at any givenpoint.

The advantages of the invention may be best understood by a discussionof a well known prior art percussive tool shown in FIG. 4. Thispercussive tool is seen to comprise a shank portion 40, a driving end 42and a recessed replaceable cutting point or tip 43 fitted on the end 42.Both the driving end 42 and the recess 45 have first and second flatsurfaces, 44, 48, and 46, 50, respectively, each having an angulardisposition relative to the main axes of the shank and tip. In assembledcondition of the shaft and tip, the first surfaces, 44 and 46,interfittingly engage and constitute a first set of tapered portionshaving a smaller taper angle, and the second surfaces, 48 and 50,interfittingly engage and constitute a second set of tapered portionshaving a greater taper angle. The second surface 50 of the tip issubstantially longer than complimentary surface 48 of the shaft leavinga non-engaged portion 52 forming a void 54, so that the shank does notbottom in the tip. The first set of interfitted surfaces, 44 and 46,serve to establish radial compressive forces that grippingly hold thetip and shaft together and the second set of interfitted surfaces, 48and 50, serve as the transmission area for the axial percussive or tooldriving forces. This construction is disadvantageous in that it does notattain 100 percent bearing of the mating surfaces and, consequently,does not provide maximum transmission of percussive forces due to thepresence of void 54 in an area extremely essential for the transmissionof such forces. Since no mating of surfaces takes place in the areabetween the extreme shank end 42 and the innermost end of recess 45,unavoidable movement of the end 42 into the recess 45 results duringoperation of the tool, and as the shank end penetrates deeper into thetip, considerable pressure is exerted onto the inner tip surface 50 bythe lowermost peripheral edge 55 of driving end 42. This pressureultimately results in a fulcrum of vector forces set up in the region ofedge 55, which, coupled with percussive vibration and frictional heatresults in fatigue of the tip material and ultimate breaking of the tip.Such breaking of the tip has been found to usually take place in thatregion of the tip indicated by reference numeral 56 where the vectorforces are most damaging. A further disadvantage of this prior artpercussive tool resides in the fact that the void 54 restricts thetransfer of heat in an area most subject to frictional heat generatedduring use of the tool. The intense heat thus concentrated between theextreme shank end and the innermost end of recess 45 anneals and softenstl 1e tip and shank end. Moreover, the heat weakens the retaining andstopping properties of the mating surfaces, allowing the shank topenetrate considerably deeper into the tip than its design allows,which, again, results in material fatigue and ultimate breaking of thetip. A still further disadvantage is that the tip 43 has an inner uppercavity diameter which generally corresponds with the outer diameter ofthe shank end 42, which considerably enhances the possibility of stressraiser forming in the shank in the upper cavity region of the tip. Alsodisadvantageous is the sharp-pointed outline of the apex 58 of the tip42 in that due to its extreme shape, the axial percussive forces workdirectly at that point causing premature material failure resulting froman extremely poor heat and force dissipation.

From the foregoing description of the invention and the discussion ofthe prior art percussive tool, the numerous advantages and improvementsincident to the invention will now be apparent to those skilled in theart.

Accordingly, the above description of the invention is to be construedas illustrative only rather than limiting. This invention is limitedonly by the scope of the following claims.

I claim 1. An impact driven tool comprising an elongated shaft having adriving end with a single substantially continuously curved conicalsurface formed by revolving a curve, and a cutting point having a recesswith a single substantially continuously curved conical surface formedby revolving a curve concentrically frictionally interengaging the shaftend surface such as to provide total mating of said surfaces relative toeach other and to effect a positive driving connection between saidshaft and said cutting point.

2. The tool as define in claim 1, wherein said driving end has asubstantially semi-elliptical external cross-sectional configuration andwherein said recess has a substantially semi-ellipti cal internalcross-sectional configuration substantially corresponding to saidexternal configuration of said driving end.

3. The tool as defined in claim 1, wherein said surfaces of said recessand said driving end include base portions and vertexes interengagingeach other.

4. The tool as defined in claim 1, wherein said cutting point includes awall area surrounding said driving end, said wall area including arelatively thin-walled portion impactively slightly stretched by saiddriving end for effecting radial compressive forces that frictionallyretain said cutting point on said driving end, and including arelatively thick-walled portion cooperating with an adjacent portion ofsaid driving end for the transmission of percussive forces from suchadjacent drive end portion to said thick-walled portion.

5. The tool as defined in claim 4, wherein said thick-walled portion ofsaid wall area includes the innermost end portion of said recess, andwherein said adjacent drive end portion includes the apex of saiddriving end abutting said innermost end portion.

6. The tool as defined in claim 1, wherein said cutting point includesan outer peripheral surface having a base portion at one end andterminating into an apex at the opposite end, and said apex constitutinga blade-shaped cutting edge.

7. The tool as defined in claim 1, wherein said cutting point includes ahardened point area and a relatively less hardened wall area surroundingsaid driving end.

8. The tool as defined in claim 1, wherein said shaft includes anextended hexagonal portion adjacent said driving end, said extendedportion having a core diameter larger than the largest diameter of saiddriving end, and wherein said shaft further includes a gradual upsetportion intermediate said extended portion and said driving end to easethe abrupt transition between such varying diameters.

1. An impact driven tool comprising an elongated shaft having a drivingend with a single substantially continuously curved conical surfaceformed by revolving a curve, and a cutting point having a recess with asingle substantially continuously curved conical surface formed byrevolving a curve concentrically frictionally interengaging the shaftend surface such as to provide total mating of said surfaces relative toeach other and to effect a positive driving connection between saidshaft and said cutting point.
 2. The tool as define in claim 1, whereinsaid driving end has a substantially semi-elliptical externalcross-sectional configuration and wherein said recess has asubstantially semi-elliptical internal cross-sectional configurationsubstantially corresponding to said external configuration of saiddriving end.
 3. The tool as defined in claim 1, wherein said surfaces ofsaid recess and said driving end include base portions and vertexesinterengaging each other.
 4. The tool as defined in claim 1, whereinsaid cutting point includes a wall area surrounding said driving end,said wall area including a relatively thin-walled portion impactivelyslightly stretched by said driving end for effecting radial compressiveforces that frictionally retain said cutting point on said driving end,and including a relatively thick-walled pOrtion cooperating with anadjacent portion of said driving end for the transmission of percussiveforces from such adjacent drive end portion to said thick-walledportion.
 5. The tool as defined in claim 4, wherein said thick-walledportion of said wall area includes the innermost end portion of saidrecess, and wherein said adjacent drive end portion includes the apex ofsaid driving end abutting said innermost end portion.
 6. The tool asdefined in claim 1, wherein said cutting point includes an outerperipheral surface having a base portion at one end and terminating intoan apex at the opposite end, and said apex constituting a blade-shapedcutting edge.
 7. The tool as defined in claim 1, wherein said cuttingpoint includes a hardened point area and a relatively less hardened wallarea surrounding said driving end.
 8. The tool as defined in claim 1,wherein said shaft includes an extended hexagonal portion adjacent saiddriving end, said extended portion having a core diameter larger thanthe largest diameter of said driving end, and wherein said shaft furtherincludes a gradual upset portion intermediate said extended portion andsaid driving end to ease the abrupt transition between such varyingdiameters.